1. Field of the Invention
This invention relates to a process for preparing an article bearing an anti-fog layer-by-layer coating and to the articles bearing an anti-fog layer-by layer coating obtained by said process, more particularly optical and ophthalmic articles, especially ophthalmic lenses for eyeglasses.
The invention is based on the use of a specific intermediate layer enhancing the adhesion of said anti-fog layer-by-layer coating, in particular on metal oxide and silicon oxide layers usually formed by vacuum deposition.
2. Description of Related Art
It is known in the art that a layer-by-layer (LbL) coating can be assembled on a substrate from species having opposite charges, typically positively and negatively charged polyelectrolytes can be alternately deposited on a substrate.
In a general manner, at least two different polyelectrolyte solutions having opposite charges, or a polyelectrolyte solution and a nanoparticle solution having opposite charges, may be used to form the LbL coating.
As known in the art, a polyelectrolyte may be a polymer having a substantial portion of its repeating units bearing an electrolyte group. These groups are ionic or ionizable groups, especially in aqueous solutions.
Other known LbL coatings include a plurality of bilayers alternately comprising oppositely charged nanoparticles.
By selecting the materials of the layers and the deposition process conditions, such films can be anti-reflective, hydrophilic or superhydrophilic, hydrophobic or superhydrophobic.
LbL coatings having hydrophilic properties may also have anti-fog properties.
US 2007/0104922 describes superhydrophilic LbL coatings that can be anti-reflective and anti-fog, such as poly(allylamine hydrochloride)/SiO2 LbL coatings.
A disadvantage of the anti-fog LbL coatings is that such coatings exhibit generally poor mechanical properties, especially poor adhesion, i.a. to mineral substrates and to metal oxides and silicone oxides layers. Mechanical properties of LbL coatings have been increased by calcination treatment, generally at high temperature (typically 550° C.).
A disadvantage associated to this technique is that it cannot be applied on any organic substrates and is only adapted to substrates that can withstand high temperature like glass substrates.
In the article “Hydrothermal Treatment of Nanoparticle Thin Films for Enhanced Mechanical Durability” Z. Gemici et al, Langmuir 2008, 24, 2168-2177, a hydrothermal treatment implemented at around 125° C., of different LbL coatings is described in order to improve mechanical durability of these coatings and avoid delamination, especially on a polycarbonate (PC) substrate.
A typical example of a LbL coating is either a polymer-nanoparticle coating made alternatively from a positively charged poly(diallyldimethyl ammonium chloride) and negatively charged silica nanoparticles, or an all-nanoparticle coating assembled alternatively from positively charged 3-aminopropyl silane modified silica (or titania) nanoparticles and negatively charged silica nanoparticles. After a hydrothermal treatment, such LbL coating has improved abrasion resistance.
US 2008/0038458 describes a hydrothermal calcination of TiO2/SiO2 LbL coatings, typically at a pressure in the range of 10 psi to 30 psi at temperature less than 500° C.
One disadvantage of the technique, along with the necessity of using an autoclave, is that the hydrothermal treatment affects the anti-fog properties of the coating, as explained in US 2008/0038458 paragraph [0046]: the coating can lose its anti-fog properties.
Consequently, it is desirable to provide a new and simple process of preparation of anti-fog LbL coatings having good or improved anti-fog properties, along with good mechanical properties such as improved adhesion to the substrate and/or improved abrasion resistance.
The adhesive function of water-borne silanes has been reported in several publications and in particular in the article “Factors contributing to the stability of alkoxysilanes in aqueous solution”, B. Ahles, J. R. Steimmetz, J. Zazyczny and P. Metha, J. Adh. Sci. Tech. 6, (1), 193, 1992. Mention of Hydrosil™ materials was made in several patents, namely U.S. Pat. Nos. 7,217,756; 6,180,244; 6,406,782; 6,372,827; 5,363,994; and 6,284,360.
There is no disclosure of the use of aminosiloxane waterbone primers in combination with an anti-fog LbL coating as the polymeric coating and no disclosure that such kind of materials can improve the mechanical properties of a LbL system without impairing the anti-fog properties of the system.